1. Field of the Invention
The present invention relates to multilayer polymer articles and process for making the same. Particularly, the present invention is directed to a multilayer polymer article with at least one layer comprising a mineral filler. The invention further discloses a method wherein the compounding, thermoforming, and product trimming processes used to form the multilayered article are accomplished sequentially in a single line.
2. Description of Related Art
The use of single or multi-layered polymer composite sheets for fabricating containers is well known. Many of the composite sheets contain layers having organic and/or inorganic fillers therein. U.S. Pat. No. 4,101,050, incorporated in its entirety by reference herein, discloses a filled polystyrene laminate containing from about 5 to 50 weight percent filler, and containers thermoformed from the laminate. U.S. Pat. No. 4,578,296, incorporated in its entirety by reference herein, discloses a cup produced by thermoforming a polyolefin resin composition sheet including a layer containing the polyolefin resin, talc filler and titanium dioxide to achieve high whiteness, and another layer containing inorganic fillers to achieve reduced luster and transparency. U.S. Pat. No. 5,143,778, incorporated in its entirety by reference herein, discloses a multilayer structure with a core layer essentially free of filler and skin layers containing fillers.
Many of the known multilayer composites can be used to form containers such as drinking cups. One conventional drinking cup preferably includes a white interior surface and a colored exterior surface. The conventional drinking cup is usually fabricated of a blend of polystyrene and high impact polystyrene. An interior layer is typically provided, which is pigmented with titanium dioxide to achieve the white, opaque surface. One drawback of the prior art container is its lack of high impact capabilities. To enhance the impact characteristics of such conventional cups, it is known to incorporate a high percentage of rubber into the formulation. Higher rubber content, however, reduces the rigidity of the container and therefore requires more material to maintain the quality of the container. Similarly, the use of higher impact property materials, such as polyolefins, often results in higher material cost due to the lower moduli of such materials. Accordingly, more polyolefin material is required to maintain the quality of the container.
A variety of methods and systems are also known for manufacturing multilayer composite articles. U.S. Pat. No. 6,120,863, incorporated in its entirety by reference herein, discloses processes to extrude a single layer structure with a single-screw extruder, and a multilayer structure with multiple single-screw extruders. This patent further notes that subsequent off-line thermoforming processes may be used to convert the extruded sheet into suitable containers. Additionally, U.S. Pat. No. 6,120,863 describes a process using compounded polymer/mica mixtures to form a composite sheet of a mineral-filled polymer. Such mineral filled polymer sheets can be extruded by a single-screw extruder equipped with a flat die using a compounded polymer/filler mixture, usually in pellet form, which is produced in a twin screw compounding extruder. A typical in-line extrusion-thermoforming process is described in U.S. Pat. No. 4,039,609, incorporated in its entirety by reference herein. This process generally consists of extruding a web of thermoplastic sheet with one or more single screw extruders to create a single or multi layered laminated sheet. The sheet is then continuously fed to a thermoforming device and subsequently trimmed.
As evident from the related art, it is desirable to produce a multilayer container having excellent rigidity and high impact properties without the need for more materials and higher costs. It is also desirable to achieve a white, opaque interior layer and pigmented exterior layer for the container while reducing material costs. To further reduce costs, it is desirable to use a more efficient and economic manufacturing process to produce a multilayer polymer article having mineral fillers therein.